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Research Document - 2014/019

Sea lice monitoring and non-chemical measures A: Biology of sea lice, Lepeophtheirus salmonis and Caligus spp., in western and eastern Canada

By Simon Jones and Stewart Johnson


Five species of sea lice (Lepeophtheirus salmonis, L. cuneifer, Caligus elongatus, C. clemensi, C. curtus) are reported from net pen-reared salmonids in Canada.  Of these, L. salmonis is the largest and most aggressive species and is the primary focus of management activities and regulations. Sea louse biology is broadly divisible into free-living and parasitic phases.  The development and survival of sea lice during both phases of development are regulated by the ambient seawater temperature and salinity. In addition, free-living stages possess numerous adaptations that permit sensing of environmental gradients of light, substances secreted by fish (semiochemicals) and mechanical energy (vibrations derived from fish movements). These adaptations enhance larval survival by optimising host-detection and settlement behaviour.  The high fecundity of adult female sea lice further optimises parasite survival. There is a wide range of susceptibilities to L. salmonis among salmonid host species in Canada indicating that sea lice survival is also mediated by host factors.  Infestations tend to be of lower intensity and of shorter duration on less susceptible species. There are significant genetic differences between the varieties of L. salmonis that occur on the Pacific and Atlantic coasts of Canada.  Further research is required to determine the biological significance of the genetic differences and to better understand the mechanisms responsible for host resistance to sea lice. This Research Document was presented and reviewed as part of the Canadian Science Advisory Secretariat (CSAS) National peer-review meeting, Sea Lice Monitoring and Non-Chemical Measures, held in Ottawa, Ontario, September 25-27, 2012. The objective of this peer-review meeting was to assess the state of knowledge and provide scientific advice on sea lice management measures, monitoring and interactions between cultured and wild fish.

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